Embodiments of the inventive concept relate generally to semiconductor memory devices. More particularly, embodiments of the inventive concept relate to flash memory devices and related program verification methods.
Flash memory devices have achieved immense popularity in recent years due to attractive features such as high storage capacity, low power consumption, and the ability to withstand physical shock. Nevertheless, users continue to demand flash memory devices with greater storage capacity and higher performance.
In an effort to improve both storage capacity and performance, researchers have developed flash memory devices with smaller features and tighter operating margins. In doing so, however, they have pushed the limits of device reliability, requiring new operating techniques to compensate for potential failures. One such technique is a programming scheme referred to as incremental step pulse programming (ISPP).
In ISPP, memory cells are programmed in a series of program loops each comprising a program section and a verification section. In the program section, a program pulse voltage is applied to selected memory cells, and in the verification section, the selected memory cells are verified to determine whether they have been successfully programmed to their target states. In successive program loops, the program pulse voltage is increased incrementally to gradually increase the threshold voltages of the selected memory cells.
Although ISPP tends to improve the reliability of programming operations, it is still prone to errors. For example, the verification section may erroneously report that a selected memory cell has been successfully programmed. As a result, the selected memory cell may contain bad data. In an effort to avoid these problems, researchers continue to seek ways to improve the reliability of verification performed in ISPP.